The present invention relates to a feature extracting method, a radiography object recognizing method and an image processing apparatus which are for processing a radiation image, and in particular, to a feature extracting method, a radiography object recognizing method and an image processing apparatus which are capable of extracting features necessary for optimum processing of a radiation image.
In recent years, there have been developed apparatuses capable of radiographing a radiation image directly as a digital image. For example, as an apparatus wherein an amount of radiations irradiated on a radiography object (subject) is detected, and radiation images formed in accordance with an amount of the detection are obtained as electrical signals, there have been disclosed many methods such as those disclosed in TOKKAISHO Nos. 55-12429 and 63-189853 employing a detector in which a stimulable phosphor is used.
In the apparatus stated above, radiations transmitted once through a radiography object are radiated on a detector in which stimulable phosphors are stuck to a sheet-like base board through coating or deposition, so that the radiations are absorbed in the stimulable phosphors.
After that, the stimulable phosphors are stimulated by light or heat energy, and thereby, radiation energy accumulated in the stimulable phosphors through the above-mentioned absorption is emitted as fluorescence light, so that the fluorescence light is subjected to photoelectric conversion to obtain image signals.
On the other hand, there has been proposed a radiation image detecting apparatus wherein electric charges corresponding to the intensity of radiated radiations are generated on a photoconductive layer, then, the generated charges are accumulated on a plurality of capacitors arranged two-dimensionally, and the accumulated charges are taken out to obtain.
The radiation image detecting apparatus of this type employs one called a flat panel detector (FPD). With regard to FDP of this type, there are known those realized by combination of A (a phosphor to emit fluorescence corresponding to the intensity of radiated radiations) and B (a photoelectric converting element such as a photodiode or CCD that receives fluorescence emitted from the phosphor directly or through a reduction optical system and conducts photoelectric conversion, as described in TOKKAIHEI No. 9-90048.
The same FDP is described also in TOKKAIHEI No. 6-342098, and there is also known one which directly converts radiated radiations into electric charges.
In these apparatuses, for the purpose of expressing radiation images with gradation that is appropriate for diagnoses, it is desirable to conduct gradation conversion automatically for images obtained on the apparatuses so that a portion to be looked by a doctor (a body part of interest, a region of interest) may be observed easily.
For the purpose of conducting this automatic gradation conversion, there is determined a processing condition such as a look-up table (LUT) wherein output signal values for input signal values are stipulated based on statistical features of image data (the greatest value, the smallest value and a histogram of the data), and thereby the gradation conversion is conducted for the entire image.
For the purpose of making the structure of details to be observed easily, there is also conducted an edge enhancement processing, and further a dynamic range compression processing for easy simultaneous observation of a high density portion and a low density portion, by highlighting edges and by narrowing a signal region of a radiography object.
However, in radiographing used for diagnoses, image processing conditions for obtaining optimum images for diagnoses vary depending on body parts radiographed, because a region to be looked by a doctor varies in radiographed body parts so as to cover many aspects from head to extremity. Further, in the same way, processing conditions also vary depending on the radiographing orientation (radiographing direction) in which the object is placed.
In these apparatuses, therefore, it has been necessary to input a body part radiographed on a radiography object and the radiographing orientation before conducting image processing so that optimum processing conditions may be selected.
Some hospitals are provided with a hospital information system (HIS) or a radiology section information system (RIS), wherein there are no operations of a radiologist in particular, and optimum processing conditions can be selected, because information of a radiographed body part can be obtained directly from order information for radiographing. In the majority of hospitals, however, these systems are not provided, and radiologists are required to input the information manually.
In the case of radiographing in a state of emergency, radiologists are sometimes required to input information of a body part on a radiography object manually even in the hospitals equipped with the above-mentioned HIS or RIS, because quick radiographing is required.
However, the number of kinds of radiographed body parts generally is 100 or more, and it is complicated to conduct the inputting operations stated above for each radiographing, which has been a burden for a radiographer who is in charge of radiographing.
For lightening the burden for the radiographer, therefore, it is required to read images obtained through radiographing to recognize a body part on a radiography object and the direction automatically, and to select the optimum processing conditions.
For judging the radiographed body part automatically, it is important to obtain precisely, from an image, a feature amount (features) that shows the radiographed body part on a radiography object.
As a method to extract a feature amount of a radiography object, there is one which extracts a feature amount from a position of a pixel showing the highest density value excluding a region of direct irradiation line irradiated directly by radiations and from a profile crossing the pixel, as that in TOKKAIHEI No. 11-96380, for example, and is used for judging whether the radiographed body part is a front side of the chest or a side of the chest.
However, the method described in the aforesaid open official gazette is persistently one for judging whether the body part is on the front side of the chest or on the side of the chest, and the method cannot be used for judgment of other body parts. Further, in radiographing used for diagnoses, it has been difficult to extract precisely a feature amount for recognizing accurately each body part radiographed, because body parts radiographed cover many aspects from head to extremity and a region to be looked by a doctor varies depending on each body part.